FIG. 1 shows a conventional hack saw having a handle and a frame fastened to the handle to hold a saw blade. The tension of the saw blade can be adjusted by a wing nut however, the angular position of the saw blade is not adjustable. U.S. Pat. No. 5,271,158, issued to the inventor of the present invention, discloses a saw blade adjusting device which permits the angular position of the saw blade to be adjusted conveniently. This saw blade adjusting device includes an adjusting link fastened to the handle to hold either end of the saw blade, a toothed locating block fastened to a front hook on the adjusting link and releasably meshed with the toothed locating block, and a spring mounted on the adjusting link and stopped between the gear and the handle. The gear can be moved backwards along the adjusting link to disengage from the toothed locating block, then rotated in either direction to turn the saw blade to the desired angle. This structure of saw blade adjusting device has drawbacks. Because the saw blade is adjusted from one end, it may be damaged easily when turned. Because the saw blade is fastened to the the handle and frame assembly by a tightening up screw rod and wing nut set, the wing nut must be loosened so that the gear can be disconnected from the toothed locating block and then rotated, the adjusting procedure is complicated. Furthermore, the limited space in the handle makes the adjustment difficult.